Electroacoustical transducer



Jan. 22, 1952 BAKER 2,582,942

ELECTROACOUSTICAL. TRANSDUCER Filed Nov. 1, 1949 Z, W HMW W? Patented Jan. 22, 1952 ELECTROACOUSTICAL TRANSDUCER Randall B. Baker, New York, N. Y., assignor to The Wheeler Insulated Wire Company, Incorporated, Bridgeport, Com. a corporation of Delaware Application November 1, 1949, Serial No. 124,898

3 Claims. 1

The present invention relates to transducers and more particularly to electro-acoustical transducers of the general type described in the patent of William J. Muldoon, No. 2,523,775, granted September 26, 1950.

The apparatus described in the Muldoon patent comprises two block shaped permanent magnets connected in series with an armature between them. Pole pieces extend outwardly from the magnets to a position near the free end of the armature where an air gap is formed. A coil which surrounds the armature within the confines of the pole pieces carries the signal current.

The object of the present invention is to provide improvements in apparatus of this general character with a particular view to maintaining an exact spacing of the pole pieces whereby an air gap of precise length is maintained. With this object in view, the invention comprises the apparatus hereinafter described and particularly defined in the claims.

In the accompanying drawings Fig. 1 is a top plan view of a transducer according to the pres ent invention; Fig. 2 is a front elevation; Fig. 3

is a side elevation, and Fig. 4 is a perspective view on a somewhat smaller scale than the other figures.

The apparatus shown in the drawings comprises two permanent magnets of rectangular block shape indicated at 8 and I0, two outwardly extending pole pieces l4 and an armature [6 secured at one end between the magnets, these parts being held together by a simple fastening means, here shown as a bolt l8. The pole pieces are bent to form front end portions l9 separated by an airgap. The armature passes through a molded coil form 20, which is preferably of nylon. A coil 22 is wound on the form.

The end of the armature extends through the form so that its end portion lies between the pole pieces, whereby a gap is formed between the armature and each of the adjacent pole pieces. The general structure thus far described is similar to that described in the above mentioned Muldoon application.

The coil form comprises a central or body portion on which the coil is wound, and end walls 24 and 26. The walls are notched at 28 and 30, respectively, to receive the pole pieces, whereby the pole pieces and the coil form may be mutually maintained in a rigid structure. The front end wall 24 of the coil form is provided with two bosses 32 which are on opposite sides of the armature. Each of these bosse is provided with a groove to receive a spacer 34. Each spacer preferably comprises a short rod of non-magnetic material, such as brass, and has a diameter equal to the desired total air gap between the pole pieces. Each rod may be retained in its grooves merely by friction, or if desired may be held in place with a drop of adhesive.

The rods are sufllciently long to extend inwardly from the bosses to be received between the ends of the two pole pieces. The armature at its front end is slightly narrower than the pole pieces, thus providing sufficient space to accommodate the ends of the spacing rods as shown in Fig. 2.

When the apparatus is assembled the spacing rods are put into position before the fastening device I8 is tight. As the fastener is tightened the pole pieces are brought into contact with the spacing rod to give an accurate determination oi the air gap. The pole pieces are preferably of such dimensions that a slight stress is applied thereto by the fastener I8, to tighten them down on the spacer rods 32 and hold the latter firmly in place. While the coil form and pole pieces are held in a rigid structure by the engagement of the pole pieces in the notches 28 and 30, no reliance is placed on said engagement for determining the air gap. Therefore, the present invention provides a simple and inexpensive means for precisely fixing the dimensions of the air gap. The apparatus is particularly useful for the rapid production of inexpensive and high-quality soundpowered telephone units.

The end of the armature may be attached by any suitable rod to a diaphragm or other means for converting between electrical and acoustic variations, as will be understood by those familiar with the transducer art.

Having thus described the invention, I claim:

1. A transducer comprising two permanent magnets, two pole pieces opposing each other across an air gap and secured to said permanent magnets, a vibrating armature fixed between the magnets and extending through the air gap, a coil form surrounding the armature and having a pair of bosses on one end thereof on either side of the air gap, each boss having a groove aligned with the desired air gap position, non-magnetic spacers seated in the grooves and extending into the air gap, and means for holding the ends of the pole pieces in contact with the spacers to maintain a fixed spatial relation between the pole pieces.

2. A transducer comprising two permanent magnets, two pole pieces secured to the magnets and having their ends opposing across an air gap, a vibrating reed fixed between the magnets and extending through the air gap, a coil form surrounding the armature having end walls notched to receive and position the pole pieces, a pair of bosses on the front end of the coil form one on each side of the air gap, each boss having a groove aligned with the desired air gap position, nonmagnetic spacers seated in the grooves and extending into the air gap, and means for holding the ends of the pole pieces in contact with the spacers to maintain a fixed spatial relation between the ends of the pole pieces.

3. A transducer comprising two permanent magnets, two pole pieces secured to the magnets with their ends opposing across an air gap, a vibrating armature fixed between said magnets and extending through the air gap, a coil form surrounding the armature with ends notched to receive and position the pole pieces, a, pair of bosses on the front end of the coil form one on each side of the air gap, each boss having a groove aligned with the desired air gap position, nonmagnetic spacers seated in the grooves extending into the air gap, and securing means passing through the pole pieces, the magnets, and the armature to stress the opposing ends of the pole pieces into contact with the spacers.

RANDALL B. BAKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

